It has been pointed out as a means for evaluating the bone strength to evaluate the bone structure. The many types of bone of a skeleton consist of cortical bones and cancellous bones, which are considered to have different bone structures and different roles, respectively. When a large load is applied to a bone, the bone is estimated to structurally act so that the cortical bone portion resists to the large load and so that the cancellous bone portion absorbs the impact.
Thereby, for the evaluation of the structure of the bone, the cortical bone portion and the cancellous bone portion must be separately and quantitatively evaluated. The cortical bones are mostly structurally continued to the cancellous bones, and it is difficult to specify the boundaries between both the bones. Hence, a bone measurement method, which enables the separation of the cortical bone from the cancellous bone in strictly good repeatability, is demanded.
On the other hand, the following bone measurement method, which enables the automatic separation of the cortical bone portion and the cancellous bone portion, has been proposed in JP-A No. 9-294740 (hereinafter, JP-A presents Japanese Unexamined Patent Publication). The method comprises separating the cortical bone portion from the cancellous bone portion by the use of the thinned images of the bone portions on the basis of the binary image of the tomographic image of a test bone, concretely a method which comprises thinning the bone portions, estimating the average bone width of the cortical bone from the outside bone portion of the thinned image, and then expanding the thinned image on the estimated value to determine the cortical bone portion.
However, the method includes a case that the cortical bone portion or the cancerous bone portion is divided, whereby a problem may be caused, when a plurality of test bones are compared with each other by the method. The present invention was achieved with respect to the problem, and the first purpose of the invention is to provide a bone measurement method which enables the stable separation of a cortical bone and a cancellous bone, even when a test bone, that is, a testee, is different, the non-invasive construction of the three-dimensional structure of bone, particularly the accurate three-dimensional evaluation of the bone, and further the high-speed and automatic separation of the cortical bone and the cancellous bone in good repeatability. Further, the second purpose of the invention is to provide a bone measurement method; which enables the stable production of the boundary surface between the cortical bone and the cancellous bone even when the testee is different, the non-invasive definition of the boundary of the bone, and the high-speed and automatic measurement of characteristics (the number, area, peripheral length and circular degree of the boundary surface) for quantitatively evaluating the characteristics of the boundary surface in good repeatability.